This invention relates generally to fusing systems for pressure fixing toners at elevated temperatures in electrostatic copying devices, and more particularly, to improved reservoir wick system for applying release agent to fuser members.
In order to affix or fuse toner material to a support surface permanently by heat, it is necessary to elevate the temperature of the toner material in order that the constituents of the toner material coalesce and become tacky. This action causes the toner to float to some extent into the fibers or pores of support members. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bounded to the support member.
Several approaches to thermal fusing of toner images onto a support material have been described in the prior art and include providing the concomitant application of heat and pressure by a roll pair maintained in pressure contact, a flat or curved plate member in pressure contact with a roll, a felt member in pressure contact with a roll, or any other suitable means. The fusing of the toner takes place when the proper combination of heat, pressure and contact time are provided, the balancing of these parameters being well known in the art and varying according to various factors.
During operation of some fusing systems, the support member is moved through the nip formed by a roll pair. By controlling the heat transfer to the toner, virtually no offset of the toner particles from the copy sheet to the fuser member is experienced under normal conditions. This is because the heat applied to the surface of the fuser member is insufficient to raise the temperature of the surface of the member above the "hot offset" temperature of the toner at which temperature the toner particles in the image areas of the toner liquefy and cause a splitting in the molten toner resulting in "hot offset". Splitting occurs when the cohesive force holding the viscous toner mass together is less than the adhesive forces tending to offset it to a contacting surface such as a fuser roll, belt, or plate. Occasionally, toner particles will be offset to the fuser roll by an insufficient application of heat to the surface (cold offsetting), by imperfection in the properties of the surface of the roll, by the toner particles insufficiently adhering to the copy sheet, by the electrostatic forces which normally hold them, or by the reactivity of the toner material itself.
One arrangement for minimizing the foregoing problems, particularly, that which is commonly referred to as offsetting, has been to provide a fuser member with an outer surface to which a release agent such as silicone oil is applied. Various polymer release materials can be used to prevent offsetting, such as disclosed in U.S. Pat. No. 3,937,637 and 3,918,804. The release agent may be applied to the fuser member by means of as described in U.S. Pat. Nos. 3,718,116, 3,831,553, and U.S. Pat. No. 3,841,827.
In using a wick assembly to apply release agent, the wick assembly often includes a felt material for absorbing and retaining the silicone oil by capillary phenomenon. The felt is then brought into into direct contact with the fixing roller or into contact with an applicator roller rotating while being in contact with the fixing roller whereby the silicone oil applied to the fixing roller. In such devices, however, often to much oil is applied and therefore the toner image is stained with oil and when ink is applied to the supporting member, the ink does not spread well. In addition, slippage often occurs between the fixing roller and the pressure roller to disturb the toner image. Also, a greater amount of oil than necessart is uneconomically consumed leading to a high frequency in which the oil supply cartridge is replaced. U.S. Pat. Nos. 3,718,116 and 3,745,972 disclose devices using a two-layer felt to reduce the amount of oil applied. However, in these systems, streak-like application irregularities tend to occur and it is very difficult to uniformly apply a small amount of oil. Another problem is that toner or paper powder or carrier particles often clog the felt whereby application irregularities are caused. In order to compensate for the above-mentioned irregularities, Japanese Laid Open patent application Nos. 110049/1977 and 37752/1979 disclose designs such that the amount of silicone oil applied to the fixing roller is controlled by non-fibrous high molecular synthetic resin having fine continuous pores. However, in the above identified disclosure, it has been confirmed that both high viscosity and low viscosity liquid is controlled by an appropriate amount and uniformly applied in the central area of said synthetic resin material with respect to the lengthwise direction of the roller, while in the opposite end portions thereof, the amount of liquid applied tends to be great. Thus, if the amount of liquid applied to the roller is great at the end portions of the synthetic resin material with respect to the lengthwise direction of the roller, this may result in slippage between the fixing roller and the pressing roller, as well as cause irregularity of the roller covered with silicone rubber, liquid contamination of the toner image supporting member and in addition, a greater amount of liquid than necessary may be uneconomically consumed.
To overcome this difficulty, U.S. Pat. No. 4,359,963 discloses an applicator that has an obstructing member for obstructing the oozing of the offset preventing liquid from the end areas of the contact with respect to the lengthwise direction of the roller. A difficulty with this type of system is that the pore size of a non-fibrous high molecular synthetic resin is not always reliable and flexible to be able to control oil flow. In addition, in the system as described in U.S. Pat. No. 4,359,963, the release agent or silicone oil is disposed above the fuser roll and the force of gravity will cause most of the oil to gather at the lower portion of the wick causing possible oil leakage and greater dispense rates.